Found this great article on building cheap practice 'cross barriers on the Cyclocross magazine site. Total cost around $15. Can't beat that with a stick. I plan to construct a set for backyard use soon. DIY rules. Click here for article and plans.
Cyclocross magazine - online and print - highly recommended. Has a bit of that homemade feel, in a good way, by folks who truly dig 'cross. Sorta like a 'cross version of Dirt Rag. Well worth checking out. Great mag.